1. Field of the Invention
The invention relates to implantable radiation therapy devices. More particularly, the invention relates to improved radiation therapy and brachytherapy devices, also known as radioactive therapeutic seeds, for the treatment of oncological and other medical conditions.
2. State of the Art
Radioactive seed therapy is a well known and well accepted medical procedure for the treatment of various oncological and other medical conditions. Seed therapy, also known as interstitial brachytherapy typically involves the implantation of one to one hundred relatively small capsules (seeds) into or around a treatment site. The capsules contain a radioactive isotope which irradiates the treatment site at close range without adversely affecting other parts of the body. Brachytherapy has been used successfully in the treatment of various types of cancers such as prostate cancer. It has also been used to prevent the growth or regrowth of tissues in the treatment of various occlusive diseases such as arteriosclerosis and arthrosclerosis subsequent to balloon angioplasty.
Radioactive therapeutic seeds are carefully designed to possess several important qualities. First, in the case of prostatic interstitial brachytherapy they should be relatively small, approximately 0.025 inch in diameter and approximately 0.16 inch long so that they may be implanted into the prostate gland using minimally invasive instruments and techniques. However, it should be appreciated by those skilled in the art that implantable radioactive sources come in all shapes and sizes. Second, the radioactive isotope must be enclosed in a biocompatible protective package since the seeds are typically not removed and will remain in the body for many years. Third, each seed preferably includes a radiopaque (e.g. high Z material) marker so that it can be located at the treatment site with the aid of fluoroscopy.
The state of the art of radioactive therapeutic seeds is substantially disclosed in seven U.S. Pat. No. 5,713,828 to Coniglione for xe2x80x9cHollow-Tube Brachytherapy Devicexe2x80x9d, U.S. Pat. No. 5,405,309 to Carden, Jr. for xe2x80x9cX-Ray Emitting Interstitial Implantsxe2x80x9d, U.S. Pat. No. 4,891,165 to Suthanthiran for xe2x80x9cDevice and Method for Encapsulating Radioactive Materialsxe2x80x9d and U.S. Pat. No. 4,784,116 to Russell, Jr. et al. for xe2x80x9cCapsule for Interstitial Implantsxe2x80x9d, U.S. Pat. No. 4,702,228 to Russell, Jr. et al. for xe2x80x9cX-Ray Emitting Interstitial Implantsxe2x80x9d, U.S. Pat. No. 4,323,055 to Kubiatowicz for xe2x80x9cRadioactive Iodine Seedxe2x80x9d, and U.S. Pat. No. 3,351,049 to Lawrence for xe2x80x9cTherapeutic Metal Seed Containing within a Radioactive Isotope Disposed on a Carrier and Method of Manufacturexe2x80x9d, which are each incorporated by reference herein in their entireties. In addition, the art has been significantly advanced in co-owned U.S. Ser. Nos. 09/133,072, 09/133,081, and 09/133,082, which are hereby incorporated by reference herein in their entireties.
The Lawrence patent, which issued in 1967, describes many of the essential features of radioactive therapeutic seeds. Lawrence describes radioactive isotopes (I-125, Pd-103, Cs-131, Xe-133, and Yt-169) which emit low energy X-rays and which have relatively short half-lives. When implanted at a treatment site, these isotopes provide sufficient radiotherapy without posing a radiation danger to the medical practitioner(s), people in the vicinity of the patient, or other parts of the patient""s body. Lawrence further describes a protective capsule which contains the isotope and prevents it from migrating throughout the body where it might interfere with healthy tissue. The capsule is cylindrical and made of low atomic number biocompatible materials such as stainless steel or titanium which do not absorb X-rays. The isotope is coated on a rod shaped carrier made of similar X-ray transparent (e.g. low Z) material and is placed inside the capsule cylinder which is then closed. The other patents each provide some improvement over the original Lawrence design.
Despite the fact that radioactive therapeutic seeds have been in use for over thirty years and despite the several significant improvements made in the seeds, many concerns still exist regarding the use of the seeds. One problem is that prior to and during implantation of the therapeutic seeds, the physician must handle the radioactive seeds, and therefore take precautions to limit his or her exposure. The precautions may include the use of lead lined clothing and limiting the time for completing any one procedure. However, such clothing is generally heavy and tiring to wear, and limiting procedure time may not be in the best interest of the patient.
In addition, it is difficult to store radioactive therapeutic seeds, as special radiation shielding materials must be used in the container storing the seeds.
Moreover, there may be situations in which it is desirable to increase the level of radiation emitted by a seed after implantation, or keep the level of radiation at a certain level, despite the natural decay of the radioactive source over a more prolonged period of time. For example, it may be desirable to provide a first dosage of radiation for a period of time and then, based upon a later diagnosis, increase the dosage for a second period of time. With the present radioactive implants of the art this can only be done through a subsequent invasive procedure of implanting additional seeds, as radioactive elements decrease their radiation output according to their respective half-life.
None of the art addresses any manner of providing an xe2x80x9cinactivexe2x80x9d seed which can later, e.g., after implantation, be activated to emit radiation. Likewise, none of the art addresses otherwise increasing the amount of radiation emitted by the seed after the seed is implanted in the patient, or maintaining a level of radiation over a longer period of time than the half-life of the radioactive isotope in the implant would otherwise permit.
It is therefore an object of the invention to provide radioactive therapeutic seeds which have means for controllably altering the radiation transmitted through the seed capsule.
It is also an object of the invention to provide radioactive therapeutic seeds which are controllably activated to xe2x80x9cturn onxe2x80x9d the seeds to cause radiation to be emitted therefrom or to increase the radiation emitted therefrom.
In accord with these objects which will be discussed in detail below, the radioactive brachytherapy seeds of the present invention generally include an outer capsule containing a radioactive material, and a substantially radiopaque shield which in a first (pre-implantation) configuration substantially obstructs radiation emitted by the radioactive material. One or both of the radioactive material and the shield are controllably movable relative to the other into a second (post-implantation) configuration such that the radioactive material is at least partially unobstructed by the shield. As a result, the level of radiation emitted by the seed is increased. For purposes herein, xe2x80x9cradiopaquexe2x80x9d refers to the property of having a relatively xe2x80x9chigh Zxe2x80x9d value, and the terms xe2x80x9cradiopaquexe2x80x9d and xe2x80x9chigh Zxe2x80x9d are used interchangeably herein.
Various embodiments of the radioactive material and the radiopaque shield are provided. In a first embodiment, a low melt temperature low Z material, e.g., wax, includes radioactive particles suspended therein. The low Z material is preferably substantially provided entirely within a high Z casing. The low Z material, with radioactive particles therein, may be heated and forced to flow, by pressurized fluid or mechanical means, through an opening in the high Z casing to at least partially surround the high Z casing and substantially cause the seed to emit radiation. In a second embodiment, an elastic or heat shrinkable casing is stretched over a radioactive material and a high Z material is deposited on the casing. When the radioactive material is heated to a melted state, the force of the casing on the radioactive material moves the radioactive material out of the casing, the casing collapses, and the radioactive material surrounds the high Z material on the casing to initiate or increase radiation emission from the seed. In a third embodiment, a flowable radioactive material is retained within a radiopaque casing by a removable barrier. The barrier may be removed by melting (e.g., a wax stopper barrier), breaking, or by a valve mechanism, and a pressurizing agent then forces the flowable radioactive material to surround the radiopaque casing. In a fourth embodiment, a first member is provided with regions upon which a radioactive isotope is deposited. The first member is disposed within a second member which includes one or more substantially radiopaque regions through which transmission of radiation is limited and one more substantially radiotransparent regions through which the radiation may be transmitted. In a first configuration, the radiopaque regions are positioned over the radioactive isotope regions. The first member may be controlled to move relative to the second member, e.g., by heat, vibration, or inertia, into a second configuration wherein the radiotransparent regions are positioned over the isotope and substantially permit the emission of radiation by the seed. In a fifth embodiment, a radiopaque shape memory alloy coil element is provided over an elongate element having an isotope deposited on a portion thereof. The rings of the coil are in a naturally compressed state over the portion of the elongate element on which an isotope is provided to prevent transmission of radiation through the rings of the coil and out of the outer capsule. The coil is trained to expand when heated and expose the portion of the elongate element provided with the isotope. In a sixth embodiment, a plurality of radiopaque shape memory alloy elements are provided, with each element having a portion on which an isotope is deposited. The portions provided with the isotope are initially oriented inward such that they do not emit radiation through the outer capsule. The elements are trained such that when they are heated, the elements change shape (or otherwise move) to substantially expose the portions provided with the isotope and thereby substantially initiate emission of radiation.
It will be appreciated that in embodiments utilizing heat to xe2x80x9cactivatexe2x80x9d the seed, the heat may be provided by hot water, microwave technology, or other radiating means provided at or near (e.g., from adjacent to a few feet away) the seed implant site. Additional means for substantially xe2x80x9cactivatingxe2x80x9d or at least increasing seed radioactivity may also be used.
It will be further appreciated that the ability to control the amount of radiation emitted by the seed enables the physician to xe2x80x9cturn onxe2x80x9d the seed or at least increase the radiation emitted by the seed when desired; i.e., upon the application of non-ambient energy, preferably of a predetermined amount. In addition, the seeds may be relatively safely handled without cumbersome precautions prior to activation.
Additional objects and advantages of the invention will become apparent to those skilled in the art upon reference to the detailed description taken in conjunction with the provided figures.